Were the enemy of the Kakurangers. Did not encounter the Zyurangers or Kibaranger at all.
Primarily fought the Mighty Morphin Power Rangers, but temporarily fought the Alien Rangers when the former were turned into children.
The monsters are modern versions of Japanese mythological beings hiding in human society, while occaisionally attacking humans. Most of them can disguise themselves as humans.
The monsters have mixed origins. Most of them are objects or living beings transformed into monsters and others are just created. A few rare monsters are acquaintances of existing characters.
Three monsters do have a human form, but these are actually humans forcibly transformed into monsters.
Were leaderless for the first 13 episodes. Were then led by Gashadokuro, who was succeeded by DaiMaOh after he died.
Were led by Rita and Lord Zedd from the start with Master Vile temporarily taking over.
Were defeated because most of them were destroyed and their leader DaiMaOh imprisoned back into the underworld. The ones that are still left are rendered powerless as gate to the underworld has been closed by the Kakurangers.
Were defeated when Zordon sacrificed himself, releasing an energy wave that turned most of the Evil Space Aliens into dust, while purifying Rita and Zedd back to human form.
Were completely new villains unrelated to previous Sentai series.
Were carried over from previous seasons of Power Rangers.